This invention relates to a semiconductor memory, more particularly, to a semiconductor memory having an information storage capacitance device comprising at least a precious metal electrode film and a ferroelectric film or an oxide film having a high dielectric constant.
The area of the information storage capacitance device has become smaller and smaller in recent years with miniaturization of semiconductor devices and the absolute value of a capacitance also tends to decrease. The capacitance C is determined by the following equation (1) in the case of a parallel flat sheet electrode structure, for example: EQU C=.epsilon..multidot.S/d (1)
where .epsilon. is a dielectric constant of dielectrics, S is the area of an electrode and d is a film thickness of the dielectrics (distance between electrodes).
To secure the capacitance without increasing the area S of the electrodes used for the information storage capacitance device, it is necessary either to use dielectrics having a high dielectric constant .epsilon. or to reduce the film thickness d of the dielectrics.
Because an inherent limit exists to the reduction of the film thickness of the dielectrics, however, technology of securing the capacitance without increasing the planar area of an insulating film used for the information storage capacitance device has been proposed as typified by a semiconductor memory using a ferroelectric such as PZT (Pb(Zr.sub.x Ti.sub.1-x)O.sub.3), etc, as the dielectrics that is described in JP-A-3-256358.
Since these ferroelectric materials are oxides and film formation is conducted under condition at a temperature of hundreds of Centigrades (.degree. C.), single-crystal silicon for fabricating a transistor, for example, cannot be used as a capacitance electrode. This is because the oxidation-reduction reaction takes place in the interface between silicon and the ferroelectric material during the film formation process or in subsequent process steps, thereby film quality of the ferroelectric film is very likely to get deteriorated.
Therefore, those materials which are difficultly oxidized even at high temperature must be used for the electrode of the ferroelectric material. The materials such as PZT have ferroelectricity only when their crystal structure is a perovskite structure. It is known empirically that crystallinity of the thin films in general having the perovskite structure is greatly affected by an underlay material.
In other words, because the material of the bottom electrode must have a function such that the perovskite thin film can grow epitaxially with the (111) or (001) texture, the lower electrode material is limited from the aspect of the crystal structure.
With the background described above, precious metal materials having a face-centered cubic structure such as platinum have been examined as the bottom electrode material. However, when a precious metal electrode is used for semiconductors, an electrically conductive film such as TiN (titanium nitride) or Ti (titanium) is necessary as a barrier layer for preventing silicon diffusion in order to prevent a silicidation reaction (chemical reaction between silicon and other metals).